In coal mining and other types of mining, it is frequently necessary for men and machines to operate in mine shafts, the roofs of which must be secured to prevent their caving in. A customary way of securing such mine shaft roofs is to install a large number of roof bolts of substantial diameter and up to ten feet long which, insofar as possible, are anchored in rock. A flexible drill shaft assembly useful in connection with drilling such mine roof holes is described in U.S. application Ser. No. 727,260 filed Feb. 10, 1977, in the name of Horace M. Varner. In addition to the flexible drill shaft assembly described in said application, some means must be provided for rotating this drill shaft as well as for moving it axially. It would be preferable if powered axial and rotational movement of the shaft can be accomplished together or independently, as conditions require. Thus it would be desirable that the drive means be capable, while rotating the shaft, of urging the shaft axially at some desired rate, at a shower rate, or perhaps not at all.
It is known to drive a drill shaft or actuating shaft in an axial direction by means of a chain drive arrangement wherein the chain meshes with the shaft and the shaft moves axially while the drive chain is carried around an endless loop. This arrangement does have the advantage that a number of links of the drive chain may be in contact with the shaft so that the driving force is not concentrated on what may be only a small line contact area on one or two links. The difficulty with this type of arrangement, however, is that it normally requires a backup plate to hold the drill shaft in mesh with the drive chain links. This type of backup plate is quite undesirable in that it adds a substantial amount of friction and wear to the drive mechanism. In U.S. Pat. No. 3,711,161 to Proctor et al is shown a means for axial drive of a beam or jib by means of a pair of coordinated driven chains, each of which has projecting means or teeth which interact with a series of apertures inside of the beam or jib to move it axially. While this double opposed type of chain drive has certain advantages over a single such unit, it would not entirely eliminate the need for backup plates or other means to hold the chain against the driven shaft or some equivalent structure to assure that the drive chain is kept in mesh with the shaft.